Adsorption air separator with dry air tap

ABSTRACT

The adsorption based air separation unit includes an adsorber vessel containing media which selectively adsorbs water vapor and nitrogen preferentially over oxygen. The vessel includes an air entry spaced from an oxygen discharge. At least one dry air tap from the adsorber vessel is located between the entry and the discharge. When the adsorption media is fresh, air entering the adsorber vessel passes through enough of the adsorber vessel to have much of its water vapor removed and only some of its nitrogen removed. The vessel can include multiple taps sequentially further from the entry which can be selectively opened as the adsorption media becomes saturated with water vapor and nitrogen, so that dry air with much of its nitrogen still present can be further tapped from the adsorber vessel. The adsorber vessel thus facilitates production of both oxygen and dry air, such as for use as medical grade air.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/974,129 filed on Dec. 18, 2015, which claims benefit under Title 35,United States Code § 119(e) of U.S. Provisional Application No.62/098,052 filed on Dec. 30, 2014.

FIELD OF THE INVENTION

The following invention relates to adsorption based air separation unitswhich produce oxygen by selective adsorption of nitrogen therefrom. Moreparticularly, this invention relates to air separation units whichproduce both oxygen and also dry air by utilizing properties ofadsorption media which adsorb water vapor and nitrogen preferably overoxygen.

BACKGROUND OF THE INVENTION

Air separation for production of oxygen or other gases is known using avariety of technologies. For instance, such technologies includeliquefaction, pressure swing adsorption and vacuum swing adsorption.

The production of oxygen using vacuum swing adsorption (VSA) iswell-known to air separation technologists. VSA offers a simplenon-cryogenic method to produce gaseous oxygen at purities of 80% to95%. In the last 20 years oxygen VSA plants have become widespread andare offered in various bed configurations. The multi-bed VSA istypically used in the size rage of 60 tons per day (TPD) and higher. Thesingle bed process was adopted as a lower capital, simpler process forlower production ranges, typically 1 TPD up to 40 TPD. Typical singlebed systems usually consist of a single blower train that is used forboth the feed air provider as well as the regeneration vacuum system.The process usually incorporates automatic valves to direct the air andvacuum flows during the cycle. A newer embodiment of the single bedprocess uses a reversing blower to generate the feed stream and applyvacuum for the regeneration step. This latest embodiment is well suitedfor small to medium sized oxygen VSA production plants (1 to 10 TPD).One example of a single bed reversing blower (SBRB) VSA process of thistype is described in U.S. Pat. No. 8,496,738.

Although the single bed reversing blower (SBRB) VSA process is simple inpractice, its simplicity comes with performance trade-offs when comparedto multi-bed systems. Firstly, the lack of additional adsorber beds doesnot allow for a crucial bed to bed equalization. The pressureequalization step is key to lowering power consumption and increasingproduct oxygen recovery. Technologists in the art have overcome thisdeficiency by adding an equalization tank to the SBRB system (such asequalization tanks in SBRB systems provided by Air Liquide of Houston,Tex.).

A need exists in some environments for both oxygen and dry air. Forinstance, in a hospital environment it is desirable to have medicalgrade oxygen as well as medical grade air. Medical grade air issubstantially dry air which can most effectively be utilized in hospitalmachinery that requires a dry air supply. This might be drive gas formedical equipment or other medical equipment which requires medicalgrade air.

SUMMARY OF THE INVENTION

With this invention a single bed reversing blower VSA system (or otherVSA system or other adsorption based air separator) is provided tosupply the medical grade oxygen (or oxygen for other uses). Thereversing blower VSA system (or other air separator) is modified to alsoprovide medical grade air (or dry air for other uses). In particular,the adsorber bed is configured with a tap off outlet a short distancefrom the inlet end of the adsorber bed. For instance, two to twelveinches from the inlet a tap is provided out of the adsorption bed. Thistap is for medical grade air. A check valve or other valve (e.g. acontrol valve) would be provided on this tap to prevent medical gradeair from being pulled back into the adsorber bed when the blowerreverses.

Molecular sieve material utilized for producing oxygen selectivelyadsorbs nitrogen in air more than oxygen. Such material also typicallyselectively adsorbs water vapor and carbon dioxide. Most typically, themolecular sieve material preferentially adsorbs water vapor even morethan nitrogen. Thus, when the material within the adsorption bed issaturated with nitrogen and the system requires that the reversingblower reverse for recharging of the adsorption bed, the molecular sievematerial is still able to adsorb more water vapor. Thus, medical gradeair can be provided from the tap throughout the VSA process.

Initially, the tap is pulling mostly air, with perhaps some increasedpercentage of oxygen, because the air is giving up water vapor more thannitrogen in the first two to twelve inches of the adsorption bed. If thetap were located further along the flow pathway within the adsorptionbed, the tap would be pulling higher and higher concentrations of oxygenin the medical grade air.

As one alternative, multiple taps can be provided into the adsorptionbed. A tap closest to the inlet would first be utilized when the bloweris providing its initial primary flow through the adsorption bed. As thebed is becoming saturated, a tap further downstream within theadsorption bed would be opened and the first tap would typically beclosed. This sequence could be further repeated with a third tap andother downstream taps. These taps could all be joined together so thatonly one medical grade air outlet from the bed is fed by each of the tapinlets. A check valve on this medical grade air line can be provided toclose when the reversing blower reverses, so that purge oxygen from apurge tank downstream of the adsorber bed is not pulled into the medicalgrade air system, and so that the vacuum created within the adsorber bedbefore final purge does not pull medical grade air back into theadsorber bed and frustrate the system's attempts to reduce pressurewithin the adsorber bed.

OBJECTS OF THE INVENTION

Accordingly, a primary object of the present invention is to provide anair separation system which both produces oxygen and dry air, such asfor supply of medical grade oxygen and medical grade air, in a singlesystem.

Another object of the present invention is to provide a method forseparating both dry air and oxygen from ambient air in an adsorptionbased air separation unit.

Another object of the present invention is to provide an apparatus whichproduces both medical grade air and oxygen, such as medical gradeoxygen, from a single air separation unit.

Another object of the present invention is to provide an adsorber vesselwhich includes an air inlet for ambient air and a discharge for oxygenand a tap for collection of dry air therefrom, so that a single adsorbervessel can be utilized for production of multiple different valuableconstituents.

Other further objects of the present invention will become apparent froma careful reading of the included drawing figures, the claims anddetailed description of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic of a prior art single bed reversing blower vacuumswing adsorption air separation unit to which the technology of thisinvention is addressed.

FIG. 2 is a schematic of a single bed reversing blower vacuum swingadsorption air separation unit incorporating a purge recovery tanktherein to enhance performance of the air separation unit and defining amodified vacuum swing adsorption air separation process according tothis invention.

FIGS. 3-5 are schematics similar to that which is shown in FIG. 2, butwith various different arrows depicting various steps in the operationof the reversing blower vacuum swing adsorption air separation unitaccording to this invention.

FIG. 6 is a schematic of a portion of the air separation unit shown inFIGS. 2-5, including the adsorber vessel, which has been modifiedaccording to this invention to include at least one dry air tap alongwith other portions of a dry air collection system.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to the drawings, wherein like reference numerals representlike parts throughout the various drawing figures, reference numeral 10(FIG. 1) is directed to a prior art oxygen separator configured toseparate/concentrate oxygen from air. This separator is modified by theair separation unit 110 of this invention (FIGS. 2-5) and the blowerdriving system 210 of this invention (FIG. 4), as explained in detailbelow.

In essence, and with particular reference to FIG. 1, basic details ofthe oxygen separator 10 modified by the air separation unit 110 andblower driving system 210 of this invention are disclosed. The oxygenseparator 10 includes an adsorber bed 20 including an adsorber materialtherein which preferentially adsorbs nitrogen, CO₂ and water overoxygen. A valve 30 is located downstream of the adsorber bed 20. Abuffer tank 40 is provided downstream of the valve 30. A blower 50defines a preferred form of pump located upstream of the adsorber bed20. A controller 60 is coupled to the valve 30 and the blower 50 (orother pump) to control opening and closing of the valve 30 and tocontrol a direction in which the blower 50 (or other pump) is operating,to either provide air into the adsorber bed 20 or pull a vacuum todesorb and remove nitrogen out of the adsorber bed 20. Normally, a heatexchanger is required between the blower and the adsorber bed to removethe heat generated when the air is compressed. The heat exchanger may bebypassed during the vacuum phase of the cycle.

With continuing reference to FIG. 1, details of the adsorber bed 20 aredescribed. The adsorber bed 20 includes an enclosure 22 for containingthe adsorber material. This enclosure 22 includes an inlet 24 spacedfrom an outlet 26. The inlet 24 and outlet 26 define preferred forms offirst and second ports for access into the enclosure 22. The inlet 24and outlet 26 normally are incorporated in closures or “end plates”which can be removed to allow access to the adsorption components in theenclosure 22. Otherwise, the enclosure 22 is preferably sealed toprevent leakage of gases into or out of the enclosure 22.

The adsorber material within the adsorber bed 20 could be any form ofmaterial which preferentially adsorbs nitrogen over oxygen. One suchmaterial is molecular sieve such as nitroxy siliporite. This material ispreferably supplied in the form of beads which are either generallyspherical in form or can be of irregular shape. Since the beads arecomposed of molecular sieve material within the enclosure 22, gaseouspathways extend through, between and around the adsorbent material.

Most preferably, a plenum is configured at the inlet and the outlet endof the adsorber bed to provide even gas flow across the cross section ofthe bed. In a preferred configuration, the inlet 24 is located below theoutlet 26, and with the inlet 24 at a lowermost portion of the enclosure22 and the outlet 26 on an uppermost portion of the enclosure 22. Theenclosure 22 could have a variety of different shapes. In oneembodiment, the enclosure 22 could be generally rectangularly shaped.The enclosure could be shaped like a pressure vessel to maximize anamount of vacuum to be drawn on the enclosure 22 while minimizing anamount of material strength (i.e. wall thickness or material choice)that must be designed into the enclosure 22. If the size of the adsorbermaterial is sufficiently small to potentially pass through the inlet 24or outlet 26, filters are provided at the inlet 24 and outlet 26 to keepthe adsorbent material within the enclosure 22.

With continuing reference to FIG. 1, details of the valve 30 aredescribed. The valve 30 is interposed on a line 32 extending from theoutlet 26 of the adsorber bed 20 and extending to the buffer tank 40.This line 32 is preferably substantially rigid, especially between thevalve 30 and adsorber bed 20, so that when a vacuum is drawn on theadsorber bed 20, the line 32 does not collapse. The valve 30 ispreferably sealed to prevent leakage in any manner when in a closedposition and to only allow passage of gas along the line 32 when in anopen position.

The valve 30 is preferably coupled to a controller 60 which controls theopening and closing of the valve 30. Optionally, the valve 30 could havea controller built into the valve 30 that could be set a single time andthen operate in accordance with its settings.

While the valve 30 would typically be programmed once and then operatein accordance with such settings, the valve 30 could optionally becontrolled at least partially through a control system including sensorsand feedback to the valve 30. For instance, an oxygen sensor could beprovided adjacent the valve 30 or along the line 32 between the valve 30and the adsorber bed 20 to detect oxygen concentration levelsapproaching the valve 30. Nitrogen adjacent the valve 30 would beindicative that the adsorbent material within the adsorber bed 30 issaturated with nitrogen and that the oxygen separator 10 needs to changeoperating modes, to have the blower 50 (or other pump) reverse to pull avacuum and desorb nitrogen from the adsorber material and pull thenitrogen out of the adsorber bed 20 to recharge the system.

Normally control of the cycle is achieved with the use of pressuretransducers which reverse the blower at appropriate times. Usually thepurge cycle is initiated when the vacuum reaches a certain predeterminedlevel. The valve 30 is then opened for a predetermined amount of time sothat a purge layer of oxygen is allowed to purge the remaining nitrogenfrom the bed. So the pressure and vacuum cycle are determined bypressure and the purge portion of the cycle is timed.

Other sensors could also potentially be utilized to allow the oxygenseparator 10 to operate most effectively. The valve 30 is preferably ofa type which operates with a minimum of lubricant or which can operatewith a lubricant which is compatible with the handling of oxygen. Thevalve 30 and other portions of the oxygen separator 10 are alsopreferably formed of materials which are compatible with the handling ofoxygen. For instance, brass is often effective in handling of oxygen andso brass is one material from which the valve 30 could be suitablymanufactured when the system 10 is used for oxygen separation.

With continuing reference to FIG. 1, details of the buffer tank 40 aredescribed. The buffer tank 40 is not strictly required for operation ofthe system, but allows for the system in the form of the oxygenseparator 10 to deliver oxygen substantially continuously, and tomoderate pressure spikes in the system. The buffer tank 40 includes anenclosure 42 with an input 44 and an output 46 in FIG. 1. However,normally the buffer tank does not have a separate inlet and outlet.Since its purpose is simply to be an accumulator and minimize thepressure fluctuations inherent in the pressure swing adsorption process.The input 44 is coupled to the line 32 on a side of the valve 30downstream from the adsorber bed 20.

The buffer tank 40 would typically have some form of regulator valve onthe output 46 which would deliver oxygen out of the buffer tank 40 whenoxygen is required by oxygen utilizing systems downstream of the buffertank 40. The input 44 of the buffer tank 40 can remain in fluidcommunication with the valve 30. The buffer tank 40 can contain oxygenat above atmospheric pressure and at a pressure matching or slightlybelow an operating pressure of the adsorber bed 20 when the adsorber bed20 is actively adsorbing nitrogen and oxygen flows into the buffer tank40.

A sensor can be associated with the buffer tank 40 which cooperates withthe controller 60 to shut off the oxygen separator 10 when the buffertank 40 nears a full condition. In many applications a compressor islocated downstream from the buffer tank 40 to fill oxygen vessels. Whenthe vessels are full the system would be shut off. If required, apressure regulator can also be provided on the output 46 of the buffertank 40 so that pressure of oxygen supplied out of the buffer tank 40remains substantially constant. Similarly, an oxygen pump could beprovided downstream of the buffer tank 40 if the oxygen were required tobe supplied at an elevated pressure above pressure within the buffertank 40.

Most preferably, the buffer tank 40 is not a particularly high pressuretank so that the oxygen separator 10 including the blower 50 (or otherpump) and adsorber bed 20 do not need to operate at a particularly highpressure when delivering oxygen to the buffer tank 40. By minimizing thepressure of the buffer tank 40, the weight of the buffer tank 40 (andother components of the system 10) can be significantly reduced.Furthermore, the power consumed by the blower is reduced as the pressuredrop across the blower is reduced.

With continuing reference to FIG. 1, details of the blower 50 (or otherpump) are described. This blower 50 generally includes a housing 52 withsome form of prime mover therein coupled to a driver, such as anelectric motor. The housing 52 of the blower 50 includes an entry 54 indirect access with a surrounding environment in a preferred embodiment.A discharge 56 is also provided on the housing 52 which is located on aside of the blower 50 closest to the adsorber bed 20.

The blower 50 is preferably in the form of a two or three lobed rotaryblower coupled in direct drive fashion to an electric motor. In oneembodiment the electric motor is a five horsepower three phase motor andthe rotary blower is a two or three lobed blower and can deliverapproximately one hundred cubic feet per minute when operating atatmospheric pressure. This rotary blower is also preferably configuredto have acceptable performance when drawing a vacuum on the adsorber bed20.

The lobes of the rotary blower are preferably configured so that theyare of approximately similar efficiency in moving gases through theblower 50 between the entry 54 and the discharge 56 in either direction.In one form, the lobes are thus symmetrical in form so that they act onthe air similarly in both directions of rotation for the blower 50.

The blower 50 is preferably substantially of a positive displacementtype so that it maintains an adequate performance when drawing a vacuumon the adsorber bed 20 so that nitrogen can be effectively desorbed fromthe adsorber material in the adsorber bed 20 when the blower 50 isoperating in a reverse direction to pull nitrogen out of the adsorberbed 20 and deliver the nitrogen out of the entry 54.

Most preferably, the blower 50 is coupled in direct drive fashion to theelectric motor (or though a gear box). Most preferably, the electricmotor is a three phase alternating current motor which can easily bereversed by reversing two of the phases. In this way, the controller 60need merely reverse two poles of the three phase motor. In an otherembodiment a direct current, permanent magnet may be used wherein thedirection of the rotation can be reversed by reversing the polaritywhich in turn will reverse the rotation of the blower. Almost all threephase electric motors are capable of being reversed as above. Directcurrent motors are also readily available from many manufacturers whichreverse their rotation direction by changing polarity.

Other types of pumps could alternatively be utilized for drawing airinto the adsorber bed 20 and pulling nitrogen out of the adsorber bed 20for the oxygen separator 10. For instance, such a pump could be apositive displacement pump, such as a piston pump or a peristaltic pump.Other forms of positive displacement pumps could also be utilizedincluding gerotor pumps, gear pumps, etc. Other forms of pumps ratherthan strictly positive displacement pumps could also be selected, suchas centrifugal pumps or axial flow pumps. The most efficient scheme forpumping the air into the system and exhausting the bed depends on therequirements of the final user.

With continuing reference to FIG. 1, details of the controller 60 aredescribed according to a preferred embodiment. The controller 60 isshown as a separate unit coupled to the blower 50 (or other pump)through a blower signal line 62 and coupled to the valve 30 through avalve signal line 64. The controller 60 could in fact be integrated intothe valve 30 or integrated into the blower 50 (or other pump) or beprovided as a standalone unit such as depicted in FIG. 1. It is alsounderstood that the controller 60 could be split into two (or more)separate devices, either separate from the blower 50 and valve 30 orintegrated into both the blower 50 and valve 30.

The controller 60 provides the basic function of controlling a directionin which the blower 50 is operating and whether the valve 30 is open orclosed. Control systems have been used which simply time the cycle. Moreoften, the controller is configured to react to pressure or some otherinput.

A preferred sequence for directional control of the blower 50 andopening and closing of the valve 30 are described in detail below. Thecontroller 60 could be in the form of a programmable logic device orcould be in the form of an application specific integrated circuit, orcould be in the form of a CPU of a special purpose computer or a generalpurpose personal computer or other computing device. The controller 60could be configured to have operating parameters set at a centralcontrolled location, such as during manufacture, or could be configuredto allow for programming in the field before and/or during operation.

In use and operation, and with particular reference to FIG. 1, detailsof the operation of the oxygen separator 10 of the prior art aredescribed. It will be understood that the separator 10 would operatesimilarly when separating other gases than when separating oxygen fromair, and the operation as an oxygen separator 10 is provided merely asone example.

Initially, the system 10 is configured with the valve 30 closed and theblower 50 (or other pump) is caused to rotate in a direction drivinggases out of the adsorber bed 20 (along arrow E). This is the vacuumcycle used to desorb nitrogen out of the beads in the bed 20. Inparticular, the blower 50 rotates to cause gases to be pulled into theentry 54 (along arrow E). This gas is removed from the bed 20 by theblower 50 and caused to pass through the discharge 54 away from theadsorber bed 20 along arrow F and to the surrounding atmosphere.

Nitrogen (or other undesirable gas) is adsorbed by the adsorber materialwithin the adsorber bed 20. Most typically, the adsorber material alsoadsorbs water vapor and carbon dioxide, as well as potentially traceamounts of other gases, including pollutants.

During the last portion of the vacuum cycle valve 30 is opened to allowa small amount of the contents of the buffer tank to be introduced intothe adsorber bed. This step is called the “purge phase.” The purge phaseis used to purge nitrogen (as well as some carbon dioxide and water outof plumbing lines and free space between the valve 30 and the blower 50,but not appreciably out into the surrounding atmosphere. This shortpurge phase is typically timed to match an amount calculated ordetermined by experiment, but could also be ended based on sensorreadings. This purge phase ends the vacuum cycle and precedes theadsorption cycle to follow.

The blower is then reversed to commence the adsorption cycle. Air isdrawn into the blower at the inlet 54 port of the blower 50 (in thedirection shown by arrow A). The air flows (along arrow B) into theadsorber bed 20 where nitrogen, carbon dioxide, and water arepreferentially adsorbed. The gas not adsorbed in the adsorber bed(normally a mixture of oxygen and argon) is passed through valve 30 intothe buffer tank 40.

The adsorber bed 20 might also adsorb oxygen to some extent. However,the adsorber material is selected so that it preferentially adsorbsnitrogen more than oxygen. Due to the presence of the adsorber materialwithin the adsorber bed 20, substantially only oxygen (or otherdesirable gas) can leave the adsorber bed 20 through the outlet 26.Typically, argon also remains with the oxygen. Because air isapproximately 1% argon and approximately 20% oxygen, this twenty to oneratio typically causes the gases being discharged from the adsorber bed20 at the outlet 26 to be approximately 95% oxygen and 5% argon.

Because the valve 30 is opened, this oxygen can flow (along arrow C)through the valve 30 and into the buffer tank 40. The buffer tank 40 isthus charged with oxygen. If oxygen is desired, it can be dischargedfrom the buffer tank 40 output 46 (along arrow D). The adsorber materialwithin the adsorber bed 20 eventually becomes saturated with nitrogenand other compounds, such as water vapor and carbon dioxide. The pointof such saturation can be calculated in advance and calibrated into theseparator 10. Alternatively, a sensor can be provided, such as along theline 32 adjacent the valve 30, to sense for nitrogen or othercontaminants within what should be substantially only oxygen and argon.Such a sensor can cause the system to detect such saturation of theadsorbent material within the adsorber bed 20 and thus change the modeof operation of the oxygen separator 10 from the adsorption cycle to thevacuum cycle. Other sensors to trigger the change could be pressuresensors or volumetric flow rater sensors either alone or in combinationwith a clock or a calibration table. The goal is to prevent nitrogen orother contaminates from passing the valve 30 after adsorption bed 20saturation.

When such saturation has either been sensed as occurring or predicted tooccur, the separator 10 changes operation modes by closing the valve 30.Then the blower 50 (or other pump) reverses its direction of operation.For instance, the controller 60 can reverse two of the three phases of athree phase electric motor coupled to the blower. The blower 50 is thencaused to turn in an opposite direction and begins pulling gas (alongarrow E) out of the adsorber bed 20 and into the blower 50 from thedischarge 56 and out of the blower 50 through the entry 54 and out intoa surrounding environment, as a repeat of the vacuum cycle describedabove.

The controller 60 can be programmed with a typical amount of timerequired to effectively desorb the nitrogen from the adsorbent materialwithin the adsorber bed 20. Normally, the controller 60 senses athreshold low pressure in the adsorber bed 20. The system operation thencontinues as described above with a short purge phase followed by returnto the desorption cycle.

This operating sequence for the oxygen separator 10 can repeat itselfpotentially indefinitely. When the buffer tank 40 becomes full (orvessels being filled from the buffer tank 40 are full), an appropriatesensor associated with the buffer tank 40 can indicate that it is fulland shut off the oxygen separator 10. As further amounts of oxygen aresensed as being needed, such as by a drop in pressure in the buffer tank40, a signal can be sent to the controller 60 to again cause the systemto commence operation.

With this invention a modified air separation unit 110 implements amodification of the prior art single bed reversing blower (SBRB) vacuumswing adsorption (VSA) oxygen separator 10 through the air separationunit 110 of this invention and the driving system 210 described in moredetail below. The SBRB VSA air separation unit (ASU) 110 is modified inthis exemplary ASU 110 to include a purge recovery tank 160. Many otherportions of the ASU 110 have analogs in the prior art SBRB VSAtechnology such as that shown in FIG. 1.

In essence, and with particular reference to FIG. 2, basic details ofthe ASU 110 are described, according to a preferred embodiment with theASU 110 also typically including many of the details of the oxygenseparator 10 as described above. A single adsorber vessel 120 is fed byan intake 130 which supplies air to the vessel 120. Downstream of thevessel 120, an O₂ supply line 125 leads to an O₂ process tank 140 whichis optionally provided to contain excess O₂ before it is utilized byequipment and/or for processes downstream of the O₂ process tank 140. Areversible blower 150 is interposed between the adsorber vessel 120 andthe intake 130. A purge recovery tank 160 is coupled to the O₂ supplyline 125 downstream of the vessel 120, preferably through a controlvalve 165 to control whether the purge recovery tank 160 is open orclosed. A compressor 170 is preferably provided downstream of the O₂process tank which can control pressure of O₂ supplied from the ASU 110.

More specifically, and with continuing reference to FIG. 2, specificdetails of the ASU 110 are described. The single adsorber vessel 120extends between an inlet 122 and an outlet 124, with the inlet 122defining a side of the vessel 120 closest to the intake 130 and theoutlet 124 on a side of the vessel 120 opposite the inlet 122. Thisvessel 120 can have any of a variety of configurations. While thisvessel 120 is described as a single adsorber vessel 120, it isconceivable that a manifold upstream and downstream of the singleadsorber vessel 120 could be provided so that multiple vessels 120 couldbe provided in parallel, but operating in unison so that the ASU 110 isstill functioning as a single bed reversing blower (SBRB) system butwith optionally additional vessels 120 merely to adjust size of thevessel 120.

The vessel 120 contains an adsorption material which preferentiallyadsorbs N₂ over O₂. This material is typically provided in the form ofbeads or other solid media which allow for gas to flow about the solidmedia as the gas extends from the inlet 122 to the outlet 124, and pastsurfaces of the adsorption material. Surfaces of the adsorption materialadsorb nitrogen thereon, allowing O₂ to pass through the vessel 120.Typically, the material within the vessel 120 also adsorbs water vaporand various other gases, while typically argon within the air is notadsorbed but passes out of the vessel 120 along with the oxygen. Thevessel 120 includes a container wall which is sufficiently strong sothat it can maintain its volume when experiencing pressures ranging fromnear vacuum at a low end to approximately atmospheric (but potentiallyslightly higher than atmospheric pressure) at a high end.

The intake 130 in a simplest form merely includes an opening which isopen to a surrounding atmosphere for intake of air into the ASU 110. Inthe embodiment depicted, the intake 130 can include some form of filterelement, such as a particulate filter and includes an air port 132spaced from a purge port 134. A valve within the intake 130 causes airto be drawn in through the air port 132 when the blower 150 is drawingair into the vessel 120, and the purge port 134 discharges gas(including mostly N₂) when the blower 150 has reversed and is pullinggas out of the vessel 120. The purge port 134 is preferably spaced fromthe air port 132 to minimize the potential for nitrogen exhaust to findits way back into the air port 132. If desired, the purge port 134 canlead to other equipment such as nitrogen recovery equipment.

Regions downstream of the vessel 120 are together generally referred tocollectively as the O₂ output in that gas of mostly O₂ remains in theseportions of the ASU 110. The O₂ process tank 140 could be avoided insystems where oxygen is used as it is produced or where discharge ofexcess O₂ beyond that utilized by the equipment downstream of the ASU110 can merely be discharged to atmosphere, or can be avoided in systemswhere downstream equipment from the ASU 110 itself includes appropriatevolume, such as in the form of tanks or other equipment so that the O₂process tank 140 is not needed. However, typically an O₂ process tank140 is provided to hold excess O₂ produced when the reversible blower150 is driving air into the vessel 120 and the ASU 110 is producing O₂,so that when the blower 150 reverses and the vessel 120 is in recoverymode and discharging nitrogen therefrom, O₂ can continue to be suppliedfrom the O₂ process tank 140 to supply downstream oxygen utilizingequipment (FIG. 4).

Most preferably, a product check valve 145 is provided upstream of theO₂ process tank 140. This check valve 145 acts to keep pressurizedoxygen within the O₂ process tank 140 and preventing back flow of oxygenback toward the vessel 120. This product check valve 145 also providesone form of valve within the O₂ supply line 125 which the reversibleblower 150 works against so that an at least partial vacuum can be drawnon the vessel 120, without significant leakage of any gases into thevessel 120 from the O₂ supply line 125. Such a vacuum is needed to allowfor recovery of the material within the vessel 120 by causing thematerial to give up the N₂ and return to a state where it is ready toagain preferentially adsorb N₂ and supply O₂ to the O₂ process tank 140.The O₂ process tank 140 includes an inlet 142 opposite an outlet 144with the inlet 142 adjacent to the product check valve 145 and theoutlet 144 leading further into equipment downstream of the ASU 110which utilize oxygen.

The reversible blower 150 includes an inlet 152 on a side of thereversible blower 150 closest to the intake 130 and an outlet 154 on aside of the reversible blower 150 opposite the inlet 152. Thisreversible blower 150 is preferably a positive displacement pump, mosttypically of a rotary lobe variety which can both efficiently blow airthrough the vessel 120 to produce oxygen, but also effectively draw avacuum on the vessel 120 when reversed. The motor coupled to the rotarylobe prime mover of the reversible blower 150 is most preferably a typeof electric motor which can readily be reversed in direction, such as byreversing a polarity of an electric field associated with the electricmotor, or some other type of electric motor which can be readilyreversed in the direction that it is operating with a minimum of stresson the equipment associated with the reversible blower 150. Typically, acontroller is coupled to the reversible blower 150 which sends a signalat an appropriate time to the reversible blower 150 to cause it toreverse from pushing air into the vessel 120 to pulling gas out of thevessel 120.

The purge recovery tank 160 is preferably provided with an openingthereinto coupled to the O₂ supply line 125, preferably at a junction162 between the outlet 124 of the vessel 120 and the product check valve145. As an alternative, the purge recovery tank 150 can be coupleddirectly to the adsorber vessel 120 typically at a portion of theadsorber vessel 120 on a side of the vessel 120 opposite the inlet 122.

A control valve 165 is interposed between the tank 160 and the O₂ supplyline 125. Alternatively, this control valve 167 can be interposedbetween the tank 160 and the vessel 120. In either configuration, thecontrol valve 165, 167 transitions from a closed state where the purgerecovery tank 160 is isolated from the O₂ supply line 125 and theadsorber vessel 120 and an open state where the purge recovery tank 160is open to the O₂ supply line 125 and/or adsorber vessel 120. Thecontrol valve 165, 167 is typically coupled to a servo motor so that itis in the form of a servo valve (SV).

The control valve 165 is coupled to a controller which can be coupled toor the same as the controller associated with the reversible blower 150,so that opening and closing of the purge recovery tank 160 occurs in asynchronized fashion with reversing of the reversible blower 150. Ifdesired, such a controller or group of controllers can also be coupledto sensors such as a nitrogen sensor which can detect trace amounts ofN₂ downstream of the vessel 120 and indicative that the material withinthe vessel 120 is approaching saturation and the need to enter arecovery phase by reversing the reversible blower 150 and drawingnitrogen out of the vessel 120 through drawing a vacuum within thevessel 120. The controller can optionally include a clock and reversethe blower (and open/close the valve 165, 167) after set amounts of timehave passed.

The compressor 170 is optionally provided downstream of the O₂ supplyline 125 and downstream of any O₂ process tank 140. Preferably acompressor check valve 175 is provided upstream of the compressor 170.The compressor 170 allows for control of a pressure desired for O₂supplied from the ASU 110. The compressor check valve 175 assists inkeeping O₂ downstream of the compressor 170 from backing up into the ASU110.

With particular reference to FIGS. 3-5, general steps in operation ofthe ASU 110 are described. FIG. 3 depicts a feed step for the ASU 110.In this step the reversible blower 150 draws air from the air intake 130through the air port 132, along arrow G. The blower 150 drives air alongarrow H into the vessel 120. The air passes through the vessel 120(along arrow I) where nitrogen is selectively adsorbed. Gas of mostly O₂flows out of the vessel 120 (along arrow J) and within the O₂ supplyline 125. The control valve 165 of the purge recovery tank 160 is closedduring the beginning of the feed step so that O₂ flow continues past thejunction 162 and through the O₂ supply line 125 (along arrow K). Theoxygen then passes through the product check valve 145 and into the O₂process tank 140 (along arrow L). Further, the O₂ can flow through thecompressor check valve 175 and through the compressor 170 for dischargefrom the ASU 110 (along arrow M).

Such a feed step (as depicted in FIG. 3) continues as long as thematerial within the vessel 120 has excess capacity for adsorption ofnitrogen. When this adsorption material within the vessel 120 becomessaturated with nitrogen, the ASU 110 needs to prepare for recharging theadsorption material within the vessel 120. To detect that suchrecharging/restoration of the material within the vessel 120 is needed,the ASU 110 can follow a timing circuit or follow gas flow valves whichmeasure an amount of gas flow, or can include a nitrogen sensor or othersensor downstream of the vessel 120 which indicate that the gasdownstream of the vessel 120 is indicative thatrecharging/reconditioning of the material within the vessel 120 isneeded.

Preparation for recovery of the material within the vessel 120 can occurin a couple of slightly different but closely related ways. In oneembodiment, such preparation begins by opening of the control valve 165(or valve 167). The interior of the pressure recovery tank 160preferably has pressure below atmospheric pressure so that gas of mostlyoxygen (but with perhaps some nitrogen present) flows quickly into thepurge recovery tank 160 through the control valve 165.

When the purge recovery tank 160 is full, or when the purge recoverytank 160 is achieving a fill level which is sufficiently great tosatisfy its purposes in purge recovery for the vessel 120, the controlvalve 165 is closed. The purge recovery tank 160 thus contains and holdsa charge of mostly O₂ (but typically with some N₂ and other contaminatespresent) as a purge charge which can be at near atmospheric pressure, orconceivably above atmospheric pressure if pressure downstream of thevessel 120 is above atmospheric pressure.

The reversible blower 150 is instructed to reverse so that air is nolonger driven into the vessel 120, but the blower 150 reverses and gasesbegin to be pulled out of the vessel 120, through the reversible blower150 and back to the intake 130. The precise moment of beginningreversing of the reversible blower 150 could be before the control valve165 associated with the purge recovery tank 160 has closed, or could beat the same time that the control valve 165 closes, or could be slightlyafter the control valve 165 closes. The reversible blower 150 typicallytakes some time to stop moving in a forward direction and then beginmoving in a reverse direction. This slow down to zero velocity and speedup in a reverse direction also define a time period which can be duringwhich the control valve 165 closes or immediately before or immediatelyafter the control valve 165 closes.

The reversible blower 150 then operates in a reverse direction drawing avacuum on the adsorber vessel 120 and portions of the O₂ supply line 125between the adsorber vessel 120 and the product check valve 145 or othervalve on the O₂ supply line 125 which resists the draw of vacuum withinthe O₂ supply line 125. Pressure is thus reduced within the O₂ supplyline 125 and the adsorber vessel 120. Gas flow through the vessel 120occurs along arrow R of FIG. 5. As the pressure is reduced within theadsorber vessel, the ability of the material within the vessel 120 tohold N₂ decreases. N₂ is thus released from the adsorber material andflows, along arrow S (FIG. 5) through the reversible blower 150 and outof the purge port 134 of the intake 130 (along arrow T of FIG. 5). Aftera sufficient amount of time and sufficiently low pressure is achievedwithin the vessel 120 to satisfactorily allow the material within thevessel 120 to recover, the ASU 110 then undergoes preparation forre-reversing the reversible blower 150 and returning the ASU 110 back tothe feed mode (FIG. 3). This preparation typically initially involvesopening of the control valve 165 (or valve 167) associated with thepurge recovery tank 160. The mostly O₂ (with some N₂) gas that has beenstored therein is thus released through the control valve 165 and intothe O₂ supply line 125 (or directly into the vessel 120 through thevalve 167 of FIG. 2).

This purge of mostly O₂ with other gases into the low pressure vessel120 allows for pressure within the vessel 120 to be quickly restored andalso for the low quality purge gas which contains some N₂ and othercontaminant gases therein to again contact the adsorption materialwithin the vessel 120 for removal of N₂ and other contaminantstherefrom. Such purge flow is generally depicted by arrow P and also bearrow Q for return back into the adsorber vessel 120 (FIG. 5).

The vessel 120 has thus been fully prepared for returning back to thefeed step. The reversible blower 150 can then be re-reversed to againdrive airflow (along arrow H of FIG. 3) from the intake 130 (along arrowG) and through the vessel 120 (along arrow I). The control valve 165with the purge recovery tank 160 can be closed just before thereversible blower 150 re-reverses, at the same time that the reversibleblower 150 re-reverses, or shortly after the reversible blower 150re-reverses.

Various factors such as the volume of gas which can reside within thevarious lines adjacent to the purge recovery tank 160 and whether theASU 110 is to be optimized for O₂ purity, energy efficiency, orproduction rate, can be factored into determining precisely when thecontrol valve 165 (or 167) should be returned to its closed state.Similar optimization can occur when determining when to initially openthe control valve 165 and also when to initially close the control valve165. The control valve 165 is re-closed so that it maintains a vacuumtherein to make the purge recovery tank 160 most effective when it isagain utilized in the next iteration of the cycle performed by the ASU110.

With particular reference to FIG. 6, details of a dry air collectionsystem 210 are described according to one embodiment of this invention.The dry air collection system 210 can be incorporated into the airseparation unit 110 (FIGS. 2-5) or could be incorporated into otheradsorption based air separation units, such as the single bed reversingblower vacuum swing adsorption system depicted in FIG. 1. Otheradsorption based air separation systems, including multiple bed systemsand non-reversing blower systems and pressure swing adsorption systemscould also provide basic systems in which the adsorber vessel 220 orsimilar vessel could be incorporated as part of a dry air collectionsystem 210 added to any such prior art adsorption based air separationtechnology.

With the dry air collection system 210, prior art adsorption vessels arereplaced with the adsorber vessel 220 (in this preferred embodiment).The adsorber vessel 220 preferably has an elongate form with oppositeends spaced apart by a side wall 228. An air entry 224 is located at oneend of the vessel 220 and an O₂ discharge 226 is provided at an end ofthe adsorber vessel 220 opposite the entry 224. The entry 224 isdownstream of a reversible blower in this embodiment and defines aportion of the adsorber vessel 220 closest to the reversible blower. Thedischarge 226 provides a discharge for oxygen from the adsorber vessel220, with the discharge 226 typically defining a portion of the adsorbervessel 220 most distant from the reversible blower 150. Adsorption media222 is located within the adsorber vessel 220. This media 222 leavesgaps between beads or other units thereof through which air/gas can passwhile coming intimately adjacent to surfaces of the media 222.

The media 222 is of a type which selectively adsorbs nitrogen overoxygen, generally in the form of an appropriate microporousaluminosilicate ziolite. Furthermore, such media 222 also selectivelyadsorbs water vapor over oxygen. Still further, and according to apreferred embodiment of this invention, the media 222 adsorbs watervapor preferentially over nitrogen. In this way, as air passes into theadsorber vessel 220 (along arrow A of FIG. 6) when it first comes intointimate position adjacent to the media 222, water vapor in the air isfirst adsorbed. As the air flows into the adsorber vessel 220, the media222 begins to become saturated with either water vapor or nitrogen,allowing the oxygen to pass on through the adsorber vessel 220 and outof the discharge 226. Over time, the media 222 becomes saturated withwater vapor and nitrogen. However, media 222 closest to the entry 224becomes saturated first, while media 222 adjacent to the discharge 226does not become saturated until late in the cycle, just before thereversible blower 150 reverses to draw a vacuum (or at least lowerpressure) on the adsorber vessel 220 to cause the release (“desorption”)of nitrogen, and water vapor from the adsorption media 222.

One can think of the adsorber vessel 220 as having multiple regions witha first region adjacent to the entry 224 and a last region adjacent tothe discharge 226. Other regions could be thought of between this firstregion and last region, such as a second region adjacent to the firstregion and a third region between the second region and the last region.Media 222 in the first region becomes saturated first, followed by mediain the second region, followed by media in the third region, and lastlysaturated in the last region and portions of the adsorber vessel 220past the last region.

Furthermore, before the first region has become saturated, the firstregion is preferentially adsorbing water vapor so that nitrogen is stillpresent in large amounts when the gas entering the adsorber vessel 220reaches the second region. The second region thus adsorbs mostlynitrogen. When the first region become saturated, the ambient airentering the adsorption vessel 220 (along arrow A of FIG. 6) remainssubstantially unmodified as it passes through the first region becausethe media 222 is saturated. When such substantially unmodified airreaches the second region, the adsorption media 222 is able to removethe water vapor preferentially over the nitrogen, with nitrogen beingadsorbed disproportionately in the third region, and leaving oxygen topass on to the discharge 226.

This process continues as the media 222 becomes progressively saturatedthereafter in the third region, and then in the last region. Thus, thegas passing from the entry 224 to the discharge 226 transitions frombeing ambient air including water vapor therein, to becoming dry air,and then before becoming largely oxygen.

With this invention, and as illustrated in this preferred embodiment, adry air tap 230 is located in the first region. This dry air tap 230 canbe opened when the adsorber vessel 220 is full of fresh media 222, sothat dry air is pulled from the dry air tap 230 (along arrow C of FIG.6). A valve 232 is located on the dry air tap 230. This valve 232 can beopened to allow dry air to pass therethrough (along arrow D of FIG. 6).The valve 232 could optionally be a check valve that is always open,except when the blower 150 reverses, to prevent back flow.

In this embodiment the dry air then passes through a compressor 240where it is pressurized and then passes (along arrow E of FIG. 6) into atank 250. This tank 250 contains substantially dry air which canfunction as medical grade air or for other purposes where dry air isneeded. The dry air is discharged through a supply 260 (along arrow F ofFIG. 6).

When the first region has become saturated, the valve 232 wouldtypically be closed so that ambient air which has not been dried of itswater vapor does not pass through the tap 230 and contaminate the dryair within the tank 250. However, the valve 232 could stay open, in thatwater vapor is still typically adsorbed even when the media 222 islargely saturated. In one embodiment of this invention, the single dryair tap 230 would be utilized for a predetermined amount of time whenthe media 222 within the adsorber vessel 220 is fresh. When the firstregion becomes saturated, the valve 232 is closed. The valve 232 is notreopened until the media 222 within the adsorber vessel 220 has beenrefreshed. As an alternative to time based control of the valve 232, amoisture sensor could be provided within the adsorber vessel 220 orwithin the dry air tap 230 upstream of the valve 232 (or conceivablydownstream of the valve 232) to sense for the presence of water vapor.When an undesirably high amount of water vapor is detected, the valve232 could be automatically closed. As another alternative, humidity ofthe ambient air could be monitored and a controller could control theopening and closing of the valve 232 based either on calculations as tohow long the valve 232 should remain open, or based on empirical valueswhich are derived from testing and experience to be appropriate times toopen and close the valve 232 for various different air humidities.

In a further embodiment of this invention, multiple auxiliary taps 270are provided downstream of the dry air tap 230. In this exemplaryembodiment, one auxiliary tap 270 is provided in each of the regionsdownstream of the first region. Each of the auxiliary taps 270preferably has its own valve 276 which feeds into a manifold line 274which passes through a junction 272 where it joins with the dry air tap230 upstream of a common compressor 240. As an alternative, it isconceivable that the multiple valves 276 could be replaced with a singlecontrol valve with four inlets and one outlet and which optionally onlyallows one inlet to be open at any given time (also typically includinga state for the valve where all taps are closed or with a separate checkvalve to prevent back flow).

When utilizing an embodiment of this invention with the dry air tap 230and the auxiliary taps 270, when the media 222 within the adsorbervessel 220 is fresh, the valve 232 would be initially open and thevalves 276 associated with the auxiliary taps 270 would all be closed.When the valve 232 is later closed, the valve 276 associated with theauxiliary tap 270 in the second region would be opened. After a furtherpredetermined amount of time, this valve would be closed and the valve276 associated with the auxiliary tap 270 in a third region would beopened. Finally, when the valve 276 in the third region is closed, thevalve 276 in the last region would be opened. At an appropriatepredetermined time, this last valve 276 in the last region would beclosed shortly before the adsorber vessel 220 undergoes recharging byreversing of the blower 150.

Throughout this process, oxygen would continue to flow (along arrow B ofFIG. 6) out of the oxygen discharge 226. When the media 222 in theadsorber vessel 220 is fresh, dry air would pass (along arrow C of FIG.6) through the dry air tap 230 while remaining air would pass toward thedischarge, have nitrogen adsorbed into the media 222, and allow oxygento flow out of the discharge 226 for collection downstream according tothe configuration of the air separation unit in which the dry aircollection system 210 of this invention is incorporated.

For versions of the system 210 that include auxiliary taps 270, when theauxiliary tap 270 in the second region is opened, dry air would flow(along arrow G of FIG. 6) into the auxiliary tap 270 in the secondregion. Thereafter, valves 276 would be closed and opened so that dryair would flow (along arrow H of FIG. 6) from the auxiliary tap 270located in the third region. Finally, valves 276 would be closed andopened so that dry air would flow (along arrow I of FIG. 6) from theauxiliary tap 270 located in the last region. While this embodiment ofthe system 210 including the auxiliary taps 270 is depicted with fourseparate taps 230, 270 total, a greater or lesser number of taps 270,230 could be provided.

With this invention, typically some nitrogen is also removed from theambient air along with the water vapor. Because the adsorption media 222preferably adsorbs water vapor preferentially over nitrogen, this amountof nitrogen adsorbed in the dry air passing through the dry air tap 230(along arrow C of FIG. 6) would be minimal. Furthermore, because air iseighty percent nitrogen approximately, even if the air loses half of itsnitrogen, it would still be a gas which has twice as much nitrogen asoxygen and would function for most purposes as dry air. With thisinvention, dry air is considered to be air which has had at least someof its water vapor removed and which has more N₂ than O₂.

To ensure that a gas without too high of a percentage of oxygen iscollecting within the tank 250, oxygen sensors can be provided tomonitor the dry air. If an excessively high oxygen content is detected,the valve 232 could be closed for a short initial period when the media222 within the vessel 220 is its very freshest, and not open until anacceptably small amount of nitrogen is being removed from the dry air.As an alternative, when nitrogen is being discharged during refreshingof the adsorber vessel 220, the valve 232 or other ones of the valves276 associated with the auxiliary taps 270 could be opened for at leasta small period of time, to draw nitrogen from the adsorber vessel 220,by action of the compressor 240 and into the tank 250. Through eithergas sensors, theoretical analysis, or empirical evidence gathered overtime, the amount of nitrogen required to be collected during thisrecharging phase for the media 222 within the adsorber vessel 220, toallow nitrogen to be pulled and added to the dry air within the tank250, can be determined and the valves 232, 276 opened for an appropriateamount of time to dilute the dry air back to having at leastapproximately eighty percent nitrogen.

In still other instances where it is acceptable to have the dry air havea greater amount of nitrogen than nitrogen present within the air, alarger amount of nitrogen can be scavenged during refreshing of theadsorber vessel 220 as disclosed above, to provide gas within the tank250 having the constituency desired. As a still further alternative,when nitrogen is removed from the adsorber vessel 220 through an inletinto the system on a side of the reversible blower 150 opposite theadsorber vessel 220, some of this nitrogen can be collected. Medicalgrade air within the tank 250 or elsewhere within the dry air collectionsystem 210 can be later analyzed and if determined to have anundesirably low amount of nitrogen therein, nitrogen collected duringthe refreshing process can be utilized to cause gas within the tank 250to meet the specifications desired.

This disclosure is provided to reveal a preferred embodiment of theinvention and a best mode for practicing the invention. Having thusdescribed the invention in this way, it should be apparent that variousdifferent modifications can be made to the preferred embodiment withoutdeparting from the scope and spirit of this invention disclosure. Whenstructures are identified as a means to perform a function, theidentification is intended to include all structures which can performthe function specified. When structures of this invention are identifiedas being coupled together, such language should be interpreted broadlyto include the structures being coupled directly together or coupledtogether through intervening structures. Such coupling could bepermanent or temporary and either in a rigid fashion or in a fashionwhich allows pivoting, sliding or other relative motion while stillproviding some form of attachment, unless specifically restricted.

What is claimed is:
 1. A system for production of oxygen and dry airfrom an adsorption based air separation unit, comprising in combination:a reversible blower adjacent to an adsorber vessel; said reversibleblower having a forward mode for drawing air into said adsorber vesseland a reverse mode for pushing gas out of said adsorber vessel; saidadsorber vessel containing an adsorption media which selectively adsorbswater vapor and nitrogen preferentially over oxygen; said adsorbervessel having an oxygen discharge spaced from an air entry, with saidair entry closer to said reversible blower than a distance from saidoxygen discharge to said reversible blower; said adsorber vessel havinga dry air tap between said air entry and said oxygen discharge; andwherein said dry air tap is one of multiple dry air taps, each said dryair tap spaced a different distance from said air entry.
 2. The systemof claim 1 wherein said adsorber vessel is elongate in form with saidair entry and said oxygen discharge located at opposite ends of saidadsorber vessel.
 3. The system of claim 2 wherein said dry air tap iscloser to said air entry than to said oxygen discharge.
 4. The system ofclaim 3 wherein said adsorber vessel has a substantially cylindricalside wall extending between said ends, said dry air tap passing throughsaid side wall.
 5. The system of claim 1 wherein a compressor is locateddownstream of said dry air tap, said compressor elevating a pressure ofgas passing from said adsorber vessel through said dry air tap.
 6. Thesystem of claim 1 wherein a dry air storage is located downstream ofsaid dry air tap.
 7. The system of claim 1 wherein at least one valve isassociated with said multiple taps, said at least one valve having an atleast partially open state and an at least partially closed state, saidat least partially closed state being more closed than said at leastpartially open state.
 8. The system of claim 1 wherein each of saidmultiple taps has a valve associated therewith, each of said valveshaving an at least partially open state and an at least partially closedstate with said at least partially open state more open than said atleast partially closed state.
 9. A method for separation of dry air andoxygen from ambient air, the method including the steps of: drawingambient air into a reversible blower and into an entry of an adsorptionbed downstream of the reversible blower, the adsorption bed containingadsorption media which selectively adsorbs water vapor and nitrogenpreferentially over oxygen; discharging oxygen from a portion of theadsorption bed spaced from the entry; drawing dry air from a dry air tapin the adsorption bed between the entry and an oxygen discharge from theadsorption bed which is further from the entry than a distance from thedry air tap to the entry; and wherein said drawing step includesmultiple dry air taps in the adsorption bed, each of the multiple tapsspaced different distances from the entry.
 10. The method of claim 9wherein said drawing step includes at least one of the dry air tapsbeing closer to the entry than to the discharge.